Prior art devices to measure blood sugar in the body non-invasively are spectroscopic devices which irradiate the body with visible, near infrared or infrared light and analyze the spectrum of either the light which passes through the body or the light reflected by it. For example, the devices disclosed in Japanese Patent Publications 3-173535 and 5-176917 project a near-infrared beam into the patient's body and estimate the concentration of glucose in the body by measuring the intensity of the light which passes through. The devices disclosed in Japanese Patent Publications 2-286132 and 4-144545 extract a small quantity of humor (body fluid) from the body and measure the concentration of glucose in this humor. In addition to these devices, various other devices have been invented to measure blood sugar either non-invasively or with very slight invasiveness, but to date none have been practically realized.
The reason why none of these non-invasive or slightly invasive devices to measure blood sugar is yet on the market becomes clear when we consider that the measurement is to be used to help diabetics control the concentration of glucose in their bodies. It is because the devices which have been invented up until now have not achieved the level of accuracy required in such an apparatus. In the conventional blood sugar measuring devices which measure the blood sugar in a non-invasive or slightly invasive manner, the absolute sugar value in the blood cannot be directly measured. In such a non-invasive device, it is necessary to know the actual length of the optical path in the body in order to measure the sugar value from the optical absorption of the light emitted by the optical device. It is, however, not possible to measure such an actual length of the optical path if the device measures only the light reflected on the skin or passed through the body. In the slightly invasive measuring device, it measures only the concentration of glucose in the humor extracted from body, but not in the blood itself. These are the reasons why there is no actual device which was released in the market.
For example, a non-invasive device using a light beam does not specifically measure the biochemical blood glucose level, but merely estimates the glucose value from the quantity of light which passes through the body. When it is affected by stray light or changes in the physiological state, the calculated result can, unfortunately, turn out to be a negative value for blood sugar or a value so large it is physically impossible. Even when a slightly invasive method is used to measure the blood sugar, large measurement errors can occur, either because such a small quantity of humor is used or because the concentration of sugar in the humor is so low.
It is, therefore, necessary to adjust the measured value in order to obtain an accurate blood sugar value with such a non-invasive type of blood sugar measuring device. It might be possible to adjust the measured sugar value manually, but it is not practical because errors may happen during the adjustment procedures or while inputting adjustment factors in the measuring device. In the prior arts, there is no automatic adjustment function to adjust the measured blood sugar value.